9310 is a far more widely used material in the metal industry than is C-158, & IF, & that's a REALLY big IF, it's heat treated correctly, it may be marginally better for an AR bolt than C-158..................but it is not mil-spec for a bolt, only C-158 is.
The issue is that since 9310 is much more readily available, basically a commodity, and not all of it is HT'd by the same HT'er with the same competency levels, there's much more variability in the stock than there is in the relatively lower volume, smaller supply based, C-158, which is more tightly controlled, but also more expensive.
And that is the reason to only buy bolts from proven & known reliable suppliers...............because they are only buying stock (or bolts) from known consistent & high quality steel suppliers.
Why do you think that companies like Anderson, Radical Firearms & Bear Creek products have a higher incidence of failure than do companies like BCM, Daniel Defense, Toolcraft, Rubber City Armory, etc., do?..................in big part, it's due to the consistency & quality of the steel.
And I ain't gonna buy jack-schitt from a company like Integrity Arms & Survival w/o a really, really good idea of who is making their parts. There's just too many other reliable options.
JMHO, YMMV
MM
